Determination of a,4-dihydroxy-3-methoxybenzeneacetic acid (vanilmandelic acid) by flow injection analysis coupled with luminol-hexacyanoferrate(III) chemiluminescence detection

A simple and robust method for the determination of the clinically significant molecule vanilmandelic acid (alpha,4-dihydroxy-3-methoxybenzeneacetic acid, 4-hydroxy-3-methoxymandelic acid) using now injection analysis with chemiluminescence detection is described. This compound was found to enhance the chemiluminescence from the reaction of luminol with hexacyanoferrate(III) in a basic medium. The calibration function obtained over the range from 2.5 x 10(-8) to 1.0 x 10(-6) mol dm(-3) approximated to linearity (r(2) = 0.9995) with the equation of best fit of y = 1.72 x 10(8) x + 36.9, where y is the integrated signal (V s) and x is the concentration (mol dm(-3)). Precision (as measured by relative standard deviation) was 2.6% for 5 replicate analyses of a standard (2.5 x 10(-7) mol dm(-3)) and the limit of detection (3 sigma) was 2 x 10(-8) mol dm(-3), Preliminary investigations revealed that the structurally similar homovanillic acid inhibits the emission of chemiluminescence from the luminol-hexacyanoferrate(III) reaction and that the kinetics of light emission were different from those of the vanilmandelic acid enhanced reaction.